1. Field
The present invention relates generally to wireless communication and more specifically to techniques for mitigating the effect of correlation in a multi-antenna wireless communication system.
2. Background
A MIMO system employs multiple (NT) transmit antennas and multiple (NR) receive antennas for data transmission. A MIMO channel formed by the NT transmit and NR receive antennas may be decomposed into NS independent channels, which are also referred to as spatial channels. Each of the NS independent channels corresponds to a dimension. The MIMO system can provide improved performance (e.g., higher throughput and/or greater reliability) if the additional dimensionalities created by the multiple transmit and receive antennas are utilized.
A multi-carrier MIMO system employs multiple carriers for data transmission. These multiple carriers may be provided by orthogonal frequency division multiplexing (OFDM) or some other construct. OFDM effectively partitions the overall system bandwidth into a number of (NF) orthogonal subbands, which are also referred to as tones, frequency bins, and frequency sub-channels. With OFDM, each subband is associated with a respective carrier upon which data may be modulated. For a MIMO system that utilizes OFDM (i.e., a MIMO-OFDM system), the MIMO channel for each of the NF subbands may be decomposed into NS independent channels, resulting in a total of NSNF independent channels.
In a wireless communication system, data to be transmitted is initially processed (e.g., coded and modulated) to form a stream of symbols. The symbol stream is then upconverted to radio frequency (RF) to generate an RF modulated signal that is more suitable for transmission over a wireless channel. For a MIMO system, up to NT RF modulated signals may be generated and transmitted in parallel from the NT transmit antennas. The NT transmitted signals may reach the NR receive antennas via a number of propagation paths and may experience different effective channels due to different effects of fading and multipath. Moreover, for a MIMO-OFDM system, the NF subbands of each transmitted signal may also experience different effective channels. Consequently, the NT transmitted signals may be associated with different complex channel gains and received signal-to-noise ratios (SNRs) that can vary across the NF subbands.
Communication systems are widely deployed to provide various communication services such as voice, packet data, and so on. These systems may be time, frequency, and/or code division multiple-access systems capable of supporting communication with multiple users simultaneously by sharing the available system resources. Examples of such multiple-access systems include Code Division Multiple Access (CDMA) systems, Multiple-Carrier CDMA (MC-CDMA), Wideband CDMA (W-CDMA), High-Speed Downlink Packet Access (HSDPA), Time Division Multiple Access (TDMA) systems, Frequency Division Multiple Access (FDMA) systems, and Orthogonal Frequency Division Multiple Access (OFDMA) systems.
There is therefore a need in the art for mitigating the effect of correlation in a multi-antenna wireless communication system.